Electric circuit breakers



' D A. T. FREEMAN 3,545,641

ELECTRIC F CI RCU'IT BREAK RR R Filed Feb. 23, 1968 2 Sheers-Sheet l D.'1970 I A. T. FREEMAN 3,546,641

' ELECTRIC CIRCUIT BREAKERS Filed Feb. 23, 1968 z SheetsSheet z FIGBUnited States Patent US. Cl. 33516 13 Claims ABSTRACT OF THE DISCLOSUREAn electric circuit breaker in which contact-separation is achieved byretracting one of a pair of co-operating contacts from the other bymeans of the force of repulsion between a conductive ring or disc and anelectromagnetic coil in which a current is suddenly caused to flow inresponse to a trip signal, the retractable contact being mechanicallyconnected to one of these members, preferably the ring or disc. Meansfor retaining the retractable contact in its retracted position andmeans for automatically releasing it on withdrawal of the other contact.A mechanical trip mechanism, responsive to the motion of the retractablecontact, for initiating withdrawal of the other contact.

BACKGROUND OF THE INVENTION This invention relates to electric circuitbreakers and is particularly, but not exclusively, applicable tosocalled high speed circuit breakers whose purpose is to achieve contactseparation as rapidly as possible on the occurrence of a trip signal,especially under overload or fault conditions, in order to be able toprovide eflicient protection in high power, direct current, circuitapplications.

An object of the invention is to provide in a circuit breaker meanswhereby contact separation may be achieved more rapidly and with lessdelay after the occurrence of a trip signal than is achievable by aknown high speed circuit breaker, such as a high speed circuit breakeraccording to our British patent specification No. 934,210, in which acertain delay is inherent in the releasing of a mechanical latch in theoperating mechanism and in which the acceleration of a movable contactaway from a cooperating stationary contact is limited by the inertia ofa relatively massive pivoted arm carrying the movable contact.

SUMMARY OF THE INVENTION The present invention makes use of thewell-known principle that when a current is suddenly caused to flow inan electromagnetic coil a repulsive force will be exerted between thecoil and a conductive ring or disc adjacent to and substantially coaxialwith the coil.

According to one aspect of the present invention, in an electric circuitbreaker comprising a pair of cooperating contacts one of the contacts ofthe pair is mechanically connected, for retraction from the othercontact, to one member of a combination comprising an electromagneticcoil and conductive ring or disc which, on the occurrence of a tripsignal in response to which a current is suddenly caused to flow in thecoil, cooperate to repel one another and thereby exert an acceleratingretraction force on the retractable contact. Preferably the member towhich the retractable contact is connected is the ring or disc and thecoil is restrained against movement, at least in the direction away fromthe ring or disc: this arrangement is conducive to fulfilling thedesideratum of minimum inertia of parts connected to the retractablecontact, as well as being more convenient for making electrical con- ICCnection to the coil, and will be assumed to subsist in order tofacilitate the following description of certain other aspects of theinvention.

It has been found that, if the ring or disc is subject to a restrainingforce inhibiting its movement away from the coil during a very shortdelay period corresponding to the inevitable time lag in the build up ofelectromag netic energy in the coil, the energy imparted to it will bemany times greater than that which would be imparted to it if not soinhibited. Such restraint may be provided by applying to the ring ordisc a biasing force which holds it against the coil and exceeds theopposing force on the ring or disc due to contact pressure exerted bythe other contact. Such biasing force (provided it is not excessive)does not decrease the force available for accelerating the retractablecontact, as might have been expected, but results in a manifold increasetherein.

With the retractable contact arranged to move rectilinearly, whichallows of a convenient arrangement with low inertia, a path for thecurrent flowing through that contact under normal working conditions andduring fault clearance is preferably provided by means of one or moresliding contacts.

Since the retraction force is transient the biasing force will returnthe contact to its closed-contact position unless means, such as a latchor toggle mechanism, is provided to retain it in a retracted position.The need for such means may be avoided by providing for withdrawal ofthe other contact of the pair from its closed-contact position prior tosuch return of the first-mentioned retractable contact; alternativelyprovision may be made both for such retention of said retractablecontact and for withdrawal of the other contact in order to achievefurther separation of the contacts. Withdrawal of the other contact maybe initiated by a release mechanism which may be actuated by anelectrical trip mechanism independently responsive to the trip signal orby a mechanical trip mechanism responsive to the motion of saidretractable contact.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may bemore fully understood, an embodiment thereof will now be described, byway of example, with reference to the accompanying drawings, in whichFIG. 1 is a diagrammatic representation of a high speed electric circuitbreaker in accordance with the invention and FIGS. 2 and 3 illustratemodifications thereof.

The circuit breaker represented by the drawings is of the kindpreviously mentioned with reference to our British patent specificationNo. 934,210 but with its stationary contact replaced by a retractablecontact as hereinbefore defined. In the following description thiscontact, 2, will be referred to as the fast contact, while the normalmovable contact 4 will be referred to as the slow contact.

The slow contact 4 is carried by a contact arm 6 which is pivoted at afixed point 8 and has an operating mechanism 10, generally as describedin said British patent specification, including a release mechanismconstituted by a latch 12 which may be of the kind described in ourBritish patent sepcification No. 849,658 with reference to FIG. 1thereof but with the arm 14 carrying the-roller 16 inverted as shown inthe present drawing. The latch 12 is releasable by the armature 17 of anelectromagnetic trip mechanism 18 (responsive to an overload current ina connection 20 to the contact arm 6 via the pivot at 8) mechanicallyconnected to the C-shaped catch 22 through the inermediary of a rod orwire 24.

In its closed posittion, as shown in the drawing, the slow contact 4bears against the fast contact 2 which is secured coaxially to the endof a rod 26 slidably mounted in a stop 28 (fixed to the circuit breakerframe partly shown at 29) through which the rod passes. Beyond the stop,the rod passes through an electromagnetic coil 30 also fixed to thecircuit breaker frame. To the other end of the rod 26 is secured, alsocoaxially, a copper ring 32 held as by a screw 34 and a clamping device36. The clamping device has a flange 36A against which bears a spiralspring 38, the other end of which bears against a fixed abutment 40 onthe circuit breaker frame. The spring may provide a force of, say, 150lbs. pressing the fast contact to the left in the drawing, as shown bythe arrow 42, against the coil 30. A main current connection 44 isconnected to the fast contact 2 through the stop 28 and a plurality ofradially spring loaded fingers 46 enabling the current path to bemaintained while the contact 2 is retracted as will now be described.

The adjustment of the contacts and the closing mechanism are so arrangedthat the slow contact presses against the fast contact, as shown by thearrow 48, with a force which may be, say, 100 lbs. Thus there is amargin of, say, 50 lbs. for opposing movement of the fast contact, whichtakes place as follows in a preferred way of operating the circuitbreaker.

An overload current, which will operate the electromagnetic tripmechanism 18 and thereby release the slow contact 4 by means of thelatch12, also causes operation of sensitive quick-acting switching meansS (such as a sensitive relay, thyratron or thyristor) which serves todischarge a previously charged capacitor C through the coil 30. Thepressure of the spring 38 retains the ring 32 in close proximity to thecoil until, after a time delay which may be less than 0.1 millisecondand is determined by the time constant of the LC circuit including theinductance of the coil 30 and the capacitance of the capacitor, a largerepulsive force established between the coil and the ring causes thefast contact to move very rapidly away from the slow contact with anacceleration which may exceed l000G; thus there is little delay betweenthe occurrence of the trip signal and the initial separation of thecontacts and there is a high rate of increase of the distance betweenthe contacts. The slow contact 4 initially attempts to follow the fastcontact 2 under the force ap plied to it by the mechanism 10 but, owingto the inertia of the arm 6, it moves much more slowly than the fastcontact. Before the slow contact has moved any appreciable distance andbefore the fast contact has returned from its excursion which may takemilliseconds, the operating mechanism 10 (its latch 12 having beenreleased by the trip mechanism 18) will have caused the slow contact 4to move away from its closed position towards its open position so thatcontact is not re-established. The use of independent electrical tripmeans for the fast and slow contacts is feasible for interruptingrapidly rising fault currents, even though the trip settings may not beabsolutely identical, because initiation of the retraction of the fastcontact is followed by a period of arcing time during which currentsubstantially in excess of the current level of the trip settings willcontinue to flow.

Contact erosion, due to wear or the effect of arcing known as burn(which would normally be accommodated by adjusting a fixed contact), isaccommodated by the slow contact the closed position of which varieswith such wear, since the repelling ring 32 connected to the fastcontact must be maintained in its correct position relatively to thecoil and with the correct pressure thereon.

The circuit breaker may incorporate a latch or toggle arrangement whichengages the fast contact 2 (or one of the parts mechanically connectedthereto) at the limit of its travel so as to prevent this contactreturning to its normal position until the latch or toggle is released.

FIG. 2 shows such a latch arrangement in which the fast-contact rod 26has an extension 26A which passes through the fixed abutment and througha conical hole 50A in another fixed member 50. This hole tapers in thedirection of return motion of the rod, opposite to the direction(indicated by the arrow 52) of retraction of the fast contact. A ring ofsteel balls 54, surrounding the rod 26A and within the hole 50A, ispressed into the tapering aperture between the rod and the conicalsurface of the hole by a light spring 56. The rod 26A is free to move inthe direction of the arrow 52 but will be gripped and held by the balls54 as soon as it attempts to return in the opposite direction. Thisaction will not be affected by any variation which may occur in thetravel of the fast contact due, for example, to variation in the voltageto which the aforementioned capacitor is charged.

FIG. 2 also shows a means of releasing such a latch. The slow-contactarm 6, in moving to its contact-open position, strikes a pin 60 carriedby a link 62 and thereby exerts a force in the link in the direction ofthe arrow 64. This force acts through a forked lever 66, pivoted at 68,to press a tubular member 70 against the ring of balls 54 in thedirection to overcome the pressure of the spring 56. With the lockingforce of the balls 54 between the rod 26A and the fixed member 50thereby removed, the retractable contact 2 is able to return to itsclosed-contact position.

Another feature with which the circuit breaker may be provided is alever arrangement responsive to the motion of the fast contact 2 andarranged to trip the latch 12 of the slow contact mechanism at apredetermined point in the travel of the fast contact. This would enablethe electromagnetic trip mechanism 18 itself to be dispensed with. Sincethe acceleration of the fast contact is very high, such lever mechanismwould be subject to severe shock loading.

FIG. 3 shows such a lever arrangement comprising a forked lever pivotedat a fixed point 82. The forked end 80A of the lever (of which only onefork is shown in the cross-sectional drawing) is so shaped andpositioned as to be acted upon, by the flange 36A against which thespring 38 bears, to rotate the lever clockwise (as indicated by thearrow 84) on retraction of the fast contact 2. The other end of thelever is coupled, by a Bowden cable 86 or other suitable means, to theslowcontact trip mechanism arm 17A which carries the armature 17, sothat the rotation of the forked lever 80- will initiate release of theslow contact 4.

The discharging of the capacitor C is preferably achieved by means of athyristor whose firing circuit PC is responsive to a signalrepresentative of the value of current flowing in the main currentcircuit being controlled by the high speed circuit breaker, so that whenthe current exceeds a predetermined value the firing circuit produces atrigger pulse which fires the thyristor. With the circuit breakercontrolling a direct current circuit, such signal may be the output of aD0. current transformer CT included in that circuit. The delay betweenthe instant at which the main current reaches the trip value and theinstant at which the thyristor is fired can be very short, typicallyless than one microsecond.

I claim:

1. An electric circuit breaker including a combination comprising anelectromagnetic coil member and a conductive ring or disc member one ofwhich members is repellably movable away from the other by sudden flowof current created in the coil member in response to a trip signal and apair of co-operating circuit-breaking contacts one of which ismechanically connected to said one of said members, whereby consequentlyupon such flow of current said one contact will be subject to anaccelerating retraction force for separating it from the other contact,including means for retaining the retractable contact in its retractedposition on completion of retraction thereof, and wherein the retainingmeans comprises a rod connected to the retractable contact for movementtherewith, a fixed apertured member having an inner surface defining atapering aperture through which the rod extends and which tapers in thedirection of movement of the rod accompanying return movement of theretractable contact to its closed-contact position, a ring of ballssurrounding the rod and being so dimensioned as to be able to contactboth the rod and said surface, and spring means urging the balls in saiddirection, the arrangement being such that when so urged the balls willco-operate with the rod and said surface to oppose movement of the rodin said direction, and wherein the release means comprises means for sourging the balls in the opposite direction to overcome the etfect ofsaid spring means.

2. An electric circuit breaker, including, in combination: anelectromagnetic coil member and a conductive ring or disc member, one ofsaid member being repellably movable away from the other of said membersby sudden flow of current created in the coil member, a pair ofco-operating circuit breaking contacts one of which is retractable andis mechanically connected to said movable one of said members, a mainsource of current electrically connected to each of said contacts andflowing through said contacts when said contacts are closed, a tripsignal source of current electrically connected to said coil member andto said main current source and adapted to create a sudden flow ofcurrent in said coil in response to undesirable variations in said maincurrent source, whereby consequently upon such sudden flow of current insaid coil said one mechanically connected contact is subjected to anaccelerating retraction force for separating it from the other contact,including means connected to said other contact for withdrawing theother contact from its closed-contact position and means for actuatingsaid withdrawing means in response to said undesirable variations andafter commencement of retraction of the retractable contact.

3. A circuit breaker as claimed in claim 2, and including means forretaining the retractable contact in its retracted position oncompletion of such retraction thereof.

4. A circuit breaker as claimed in claim 2, wherein the circuit breakerincludes automatic release means for releasing the retaining means inresponse to movement of said other contact on such withdrawal thereof.

5. A circuit breaker as claimed in claim 1, wherein means areincorporated for withdrawing the other con tact from its closed-contactposition and automatic release means for releasing the retaining meansin response to movement of said other contact on such withdrawalthereof, the release means comprising a tubular member surrounding therod and capable of being urged against the balls in said oppositedirection, pivotally mounted lever means for so urging the tubularmember, and link means for transmitting to the lever means movementimparted to the link means by said other contact on withdrawal thereof,the movement being such as to cause such urging of the balls as toovercome the effect of said spring means.

6. The combination claimed in claim 5, wherein means are included forWithdrawing the other contact.

7. A circuit breaker as claimed in claim 6 including a mechanical tripmechanism, said mechanism responsive to the motion of the retractablecontact on retraction thereof, and means for initiating the action ofthe withdrawing means.

8. The combination as claimed in claim 2, wherein there is included atrip mechanism operatively connected to said withdrawing means toinitiate the action of the said withdrawing means before the return ofsaid retractable contact to its closed-contact position.

9. The combination claimed in claim 8, wherein the said trip mechanismincludes an electrical trip mechanism electrically connected to saidtrip signal source and a mechanical trip mechanism mechanicallyresponsive to the motion of said retractable contact on retractionthereof, and wherein the electrical and mechanical trip mechanismsinclude a common lever for transmitting their initiating etfect to thewithdrawing means.

10. The combination of claim 2 wherein the retractable contact movesrectilinearly.

11. The combination of claim 10 wherein there is included in cooperativeelectrical relation one or more sliding contacts, a stationaryconductive member electrically connected to said one or more slidingcontacts, said contacts providing an electrical connection between saidretractable contact and said stationary conductive member.

12. The combination of claim 2 and including time delay circuit meanselectrically connected to said trip signal source and said coil andmeans for subjecting said movable member to a restraining forceinhibiting movement thereof during the delay period of said time delaymeans.

13. The combination of claim 12 and wherein further first means areprovided for forcing said withdrawable contact against said retractablecontact and second means for forcing said retractable contact againstsaid withdrawable contact, said second forcing means exceeding saidfirst forcing means by an amount equal to said restraining force.

References Cited UNITED STATES PATENTS 1,818,801 8/1931 Herden 335-1922,486,104 10/1949 Bohn 335-14 3,127,488 3/1964 Bodenschatz 335-1743,178,533 4/1965 Lory 335-174 3,215,798 11/1965 Kesselring 335-383,384,845 5/1968 Johnson 335-16 FOREIGN PATENTS 740,568 1/1933 France35-16 BERNARD A. GILHEANY, Primary Examiner H. BROOME, AssistantExaminer US. Cl. X.R. 317-11

